Liquid crystal display apparatuses utilize video data to display images on a liquid crystal display section. The video data is corrected through data correction such as gamma correction on the control circuit of the liquid crystal display apparatus. A lookup table (LUT) is generally utilized for the data correction. In many cases, LUT is a RAM, which is rewritable, in order that parameters in the LUT may be changed according to different data correction. In this arrangement, video correction data stored in an external ROM in advance is transferred to the LUT before display.
However, the liquid crystal display apparatuses of this arrangement would suffer from destruction of data in the LUT due to noise due to static electricity, etc. during display. Destroyed data in the LUT makes it impossible to perform intended data processing.
As a solution, a method in which the ROM refreshes the LUT in order to restore the destroyed data in the LUT has been already disclosed. This method is described below with reference to FIGS. 9 and 10. This method is, for instance, shown in Japanese Unexamined Patent Publication No. 237519/1996 (Tokukaihei 8-237519 (Date of publication: Sep. 13, 1996)).
FIG. 9 illustrates a control circuit which corrects the video data in conventional liquid crystal display apparatus. The control circuit comprises a data operation section 80, an LUT 81, and a ROM 82 as illustrated in FIG. 9.
Video correction data whose content is identical to that of the data stored in the LUT 81 is stored in the ROM 82 in advance. An input data signal externally inputted into the data operation section 80 is corrected and then outputted as an output data signal.
The LUT 81 communicates with the data operation section 80 during display intervals. Video correction data whose content is identical to that of the data stored in the LUT 81 is stored in the LUT 82 in advance. The video correction data is transferred from the ROM 82 to the LUT 2 to update (refresh) the video correction data in the LUT 2 during vertical blanking intervals.
The timing for video data correction utilizing the control circuit in FIG. 9 is described below with reference to the timing diagram of FIG. 10. In this diagram: t51-t52, t53-t54, and t55-t56 are the display intervals; t52-53 and t54-t55 are horizontal blanking intervals; and t56-t57 is a vertical blanking interval.
During the display intervals on the waveform (x), the data operation section 80 communicates with the LUT 81. Corrected video data is subsequently outputted through the data operation section 80. Intervals other than the display intervals are blanking intervals: the horizontal blanking intervals and the vertical blanking intervals. As the waveform (x) indicates, a blanking interval and a display interval alternate.
Control signal (sixth control signal) between the ROM 82 and the LUT 81, as the waveform (y) indicates, is at ‘L’ level during the vertical blanking intervals while the control signal is at ‘H’ level during the display intervals and the horizontal blanking intervals.
Specifically, as indicated by the waveform (x), shifting from the vertical blanking interval to the display interval occurs at the time t51. The access from the data operation section 80 to the LUT 81 is turned on upon shifting the vertical blanking interval to the display interval. At the same time, as the waveform (y) indicates, the sixth control signal rises to ‘H’ level. At the time t52, as the waveform (x) indicates, the access from the data operation section 80 to the LUT 81 is turned off upon shifting the display interval to the horizontal blanking interval. At this point, as the waveform (y) indicates, the sixth control signal remains at ‘H’ level. At the time t53, as the waveform (x) indicates, the access from the data operation section 80 to the LUT 81 is turned on upon shifting the horizontal blanking interval to the display interval. At this point, as the waveform (y) indicates, the sixth control signal remains at ‘H’ level.
Shifting the display interval to the horizontal blanking interval occurs at the time t54, as indicated by the waveform (x). The access from the data operation section 80 to the LUT 81 is turned off upon shifting the display interval to the horizontal blanking interval. At this point, as the waveform (y) indicates, the sixth control signal remains at ‘H’ level. At the time t55, as the waveform (x) indicates, the access from the data operation section 80 to LUT 81 is turned on upon shifting the horizontal blanking interval to the display interval. At this point, as the waveform (y) indicates, the sixth control signal remains at ‘H’ level. At the time t56, as the waveform (x) indicates; shifting the display interval to the vertical blanking interval occurs. The access from the data operation section 80 to the LUT 81 is turned off upon shifting the display interval to the vertical blanking interval. At the same time, as the waveform (y) indicates, the sixth control signal falls to ‘L’ level.
Only during the vertical blanking intervals, the video correction data is transferred from the ROM 82 to the LUT 81. In other words, the video correction data in the LUT 81 is updated (rewritten, refreshed) during every vertical blanking interval. Therefore, the control circuit can normally correct video data even if the data in the LUT 81 is destroyed due to noise due to static electricity.